As a consequence of the uncertainties in this global assessment, its quantitative results cannot be confidently extrapolated to smaller geographic areas, such as specific countries or cities. The methods for estimation of exposure and extrapolation of concentration-response functions were developed specifically for estimating burdens for large geographic regions, often in
the absence of essential data on exposure and response. Where better data exist, as they currently do in some parts of the world, they should of course be used.